From patchwork Tue Jun 16 16:33:39 2015 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Igor Mammedov X-Patchwork-Id: 6618981 Return-Path: X-Original-To: patchwork-kvm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.136]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 52A749F40A for ; Tue, 16 Jun 2015 16:33:59 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 6D51C20618 for ; Tue, 16 Jun 2015 16:33:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7725A206F0 for ; Tue, 16 Jun 2015 16:33:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756670AbbFPQdz (ORCPT ); Tue, 16 Jun 2015 12:33:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43199 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756616AbbFPQdt (ORCPT ); Tue, 16 Jun 2015 12:33:49 -0400 Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) by mx1.redhat.com (Postfix) with ESMTPS id 8DB732CD85E; Tue, 16 Jun 2015 16:33:49 +0000 (UTC) Received: from dell-r430-03.lab.eng.brq.redhat.com (dell-r430-03.lab.eng.brq.redhat.com [10.34.112.60]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id t5GGXfdO001342; Tue, 16 Jun 2015 12:33:48 -0400 From: Igor Mammedov To: linux-kernel@vger.kernel.org Cc: mst@redhat.com, kvm@vger.kernel.org, pbonzini@redhat.com Subject: [PATCH 5/5] vhost: translate_desc: optimization for desc.len < region size Date: Tue, 16 Jun 2015 18:33:39 +0200 Message-Id: <1434472419-148742-6-git-send-email-imammedo@redhat.com> In-Reply-To: <1434472419-148742-1-git-send-email-imammedo@redhat.com> References: <1434472419-148742-1-git-send-email-imammedo@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org X-Spam-Status: No, score=-7.5 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP when translating descriptors they are typically less than memory region that holds them and translated into 1 iov enty, so it's not nessesary to check remaining length twice and calculate used length and next address in such cases. so relace a remaining length and 'size' increment branches with a single remaining length check and execute next iov steps only when it needed. It saves tiny 2% of translate_desc() execution time. Signed-off-by: Igor Mammedov --- PS: I'm not sure if iov_size > 0 is always true, if it's not then better to drop this patch. --- drivers/vhost/vhost.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 68c1c88..84c457d 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -1111,12 +1111,8 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len, int ret = 0; mem = vq->memory; - while ((u64)len > s) { + do { u64 size; - if (unlikely(ret >= iov_size)) { - ret = -ENOBUFS; - break; - } reg = find_region(mem, addr, len, &vq->cached_reg); if (unlikely(!reg)) { ret = -EFAULT; @@ -1124,13 +1120,22 @@ static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len, } _iov = iov + ret; size = reg->memory_size - addr + reg->guest_phys_addr; - _iov->iov_len = min((u64)len - s, size); _iov->iov_base = (void __user *)(unsigned long) (reg->userspace_addr + addr - reg->guest_phys_addr); + ++ret; + if (likely((u64)len - s < size)) { + _iov->iov_len = (u64)len - s; + break; + } + + if (unlikely(ret >= iov_size)) { + ret = -ENOBUFS; + break; + } + _iov->iov_len = size; s += size; addr += size; - ++ret; - } + } while (1); return ret; }